WAEC Chemistry 2014 Paper

Concept:Le Chatelier’s principle states that a change in pressure shifts the equilibrium toward the side having fewer gas moles.Explanation:Consider the reaction:$$\mathrm{N}_{2(g)} + 3\mathrm{H}_{2(g)} \rightleftharpoons 2\mathrm{NH}_{3(g)}; \quad \Delta H^\ominus = -x\ \mathrm{kJ\,mol^{-1}}$$The reactant side contains $1 + 3 = 4$ moles of gas.The product side contains $2$ moles of gas.The forward reaction is exothermic and reduces the total gas moles from 4 to 2.Increasing the total pressure causes the equilibrium to shift toward fewer gas moles, which is the forward direction.This increases the production and yield of $\mathrm{NH}_3$.Answer:D. Increase in the total pressure of the system